1. Field
The present disclosure relates to an apparatus and method for compensating an image of a display device.
2. Description of the Related Technology
Flat plate display types include a liquid crystal display (LCD), a field emission display, a plasma display panel (PDP), and an organic light emitting display device.
The organic light emitting display device generally displays an image using an organic light emitting diode that emits light by recombination of electrons and holes. Such an organic light emitting display device is driven with low power while having a fast response speed, has an excellent merit in luminance efficiency, luminance, and a viewing angle and thus has been in the spotlight recently.
In general, organic light emitting display devices are classified into a passive matrix organic light emitting diode (PMOLED) and an active matrix organic light emitting diode (AMOLED) according to a method that drives an organic light emitting diode.
The PMOLED is a method of forming a positive electrode and a negative electrode to be orthogonal and selecting and driving a negative electrode line and a positive electrode line, and the AMOLED is a driving method of integrating a thin film transistor and a capacitor within each pixel and enabling to sustain a voltage by a capacitance. The PMOLED has a simple structure and is driven with a cheap cost, but cannot realize a panel of a large size or high definition. The AMOLED can realize a panel of a large size and high definition, but there is a problem that a control method thereof is technically difficult and the AMOLED is relatively expensive.
An AMOLED selectively emits light in each unit pixel in view of a resolution, a contrast, and an operation speed.
In a pixel of an AMOLED (hereinafter, an organic light emitting display device), a light emitting degree of an organic light emitting diode (OLED) is adjusted by controlling a driving transistor that supplies a driving current according to a data voltage to the OLED.
A deviation in a threshold voltage and current mobility between a plurality of driving transistors may occur within a display panel of the organic light emitting display device. Such a deviation may occur according to poly-silicon characteristics and a production process, a production method, and/or an environment of a driving transistor. Alternatively, such a deviation may occur by deterioration of a driving transistor according to increase of a use time (display period) of the organic light emitting display device.
Due to non-uniform threshold voltage characteristics of a driving transistor, even if the same threshold voltage is applied to each pixel circuit, a light emitting degree of an output pixel becomes different and thus a stain phenomenon like a relatively dark sand grain occurs on a bright screen. That is, when a threshold voltage of a driving transistor is not uniform, even if the same data voltage is applied, a gate-source voltage (Vgs) output of a driving transistor that is directly related to a driving current that is supplied to an OLED becomes different. Therefore, an image is not expressed with accurate grayscale according to a data signal, stain occurs, and a display quality is deteriorated.
Technology that compensates an image through threshold voltage scattering compensation of such a driving transistor has been developed, but nowadays, a display panel is formed in a large size and thus in a trend in which a high speed driving method is requested, it is difficult to fully compensate a threshold voltage of a pixel of an entire display panel.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.